Downhole torque limiter and method

ABSTRACT

The downhole torque limiter and method eliminate damage to downhole components by eliminating excessive torque transmission. The device comprises a housing, compression assemblies, and anti-rotation plates. Inner and outer assemblies of the device are permitted to slip with respect to each other after reaching a settable torque limit which is preferably below the maximum capacity of other downhole components. The device may be positioned in drill strings that comprise a downhole motor and/or drill bit as well as drill strings that do not comprise a downhole motor and/or drill bit. In drill strings comprising a downhole motor and/or drill bit, the device may be positioned below the downhole motor and above the drill bit, adjacent to and above the downhole motor, or above the downhole motor such that at least one drill string joint is positioned between the device and the downhole motor.

This application claims benefit from U.S. Provisional Patent Application No. 61/529,975, filed Sep. 1, 2011.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to drill strings and related equipment as typically used in the oil and gas industry. More specifically, this invention relates to a device and method that limit torque transmission such that equipment is protected from overload and damage.

2. Description of the Prior Art

Drilling and well service operations may be performed with a rotating or non-rotating drill string composed primarily of tubular members and which may also contain a fluid driven downhole motor. Torque is delivered from the surface to the bit, mill, or other device via transmission through the drill string. If utilized, a downhole motor provides additional torque and rotation near the bit, mill, or other device by converting hydraulic energy from the drilling fluid into mechanical power.

Drilling or milling torque is typically a result of the aggressiveness of the drill bit or mill and the axial load at which it is forced into the bottom hole or object. If a downhole motor is utilized and sufficient force is applied, the downhole motor may stall such that the downhole motor is no longer capable of turning the bit. Such stalling events are well known and may cause severe damage to the downhole motor and other equipment.

In addition, the drill string and associated equipment may be subjected to excessive torque due to many other sources such as obstructions and improper procedures. Another well known event that may subject portions of the drill string to excessive torque loading are torsional vibrations or stick-slip in which the drill string tends to wind up and release. Such events may cause substantial damage to certain components including but not limited to threaded connections. A particular undesirable result may include twist off failure of threaded connections.

Various tools have been proposed which address the problems thus described. Some such tools incorporate a mandrel which tends to retract within a collar or housing with a given rate or when subjected to excessive torque. Other such tools provide mechanical means of relieving torque transmission. Typically, such tools are of complicated construction and are subject to various undesirable limitations.

Various other tools may contain shearing mechanisms which provide relief from excessive torque. This action then typically requires the device and the entire drill string to be removed from the wellbore for repair. Such occurrences are undesirable in practice.

SUMMARY OF THE INVENTION

The present invention provides an axial load and pressure compensated torque limiting device that may be positioned between upper and lower portions of a drill string. When torque between the two portions exceeds a predetermined limit, relative rotation is permitted, thus limiting torque transmission. Relative rotation between the upper and lower sections is preferably resisted by frictional forces between various plates that are compressed together and, thus, preset by axial pressure. Such plates are preferably rotatably restrained to the upper and lower extremities of the device in an alternating pattern via external and internal interfaces. A compensation system is provided to compensate for varying axial pressure, such that external compressive and tensile loads do not alter the axial pressure applied to the plates and, thus, the friction between them. In a preferred embodiment, such a compensation system comprises preloaded spring assemblies which tend to maintain constant pressure between contacting plates. A bore connecting the upper and lower extremities is provided, thus, permitting free passage of fluids.

Plates and surfaces subject to rubbing and chaffing between themselves are preferably constructed of or coated by a resilient material which is abrasion resistant. Such materials or coatings may include hardened steel alloys, tungsten-carbide, and cobalt-chromium, amongst many others.

In one embodiment, an upper threaded connection comprises a portion of a tubular upper housing connected to the outer collar via another threaded connection.

In another embodiment, the tubular upper housing may provide an internal shoulder which abuts with an upper spring or spring assembly comprising one or more coil springs.

In one embodiment, the uppermost outer friction plate axially abuts an inner friction plate, such inner and outer plates alternate until terminated by a final outer friction plate which axially abuts a ring fixed to the inner mandrel.

In one embodiment, one or more of the friction plates comprise polygonal profiles.

In one embodiment, one or more of the friction plates comprise rounded profiles.

In one embodiment, the assembly comprises a ring and a static ring wherein the ring is coupled to the inner mandrel and rests axially against the static ring which is rotatably coupled to the outer collar.

In one embodiment, the upper and lower spring assemblies comprise one or more coil springs.

In one embodiment, the upper and lower spring assemblies comprise a combination of one or more coil springs and/or disc springs.

In one embodiment, a threaded connection is provided within the lower portion of the lower mandrel for cooperative coupling with a bit, mill, or other device.

In another embodiment, compression of the upper spring assembly is adjusted by a jam nut arrangement.

In another embodiment, compression of the upper and lower spring assemblies is adjusted by one or more shims.

In one embodiment, the downhole torque limiter may be oriented within the bottom hole assembly below the downhole motor and above the bit.

In one embodiment, the downhole torque limiter may be oriented within the bottom hole assembly above the downhole motor and above the bit.

In another embodiment, the downhole torque limiter may be oriented at any point within the drill string where it is desired to limit the maximum torque transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view of the downhole torque limiter in accordance with a preferred embodiment.

FIG. 2 is a cross-sectional view of the downhole torque limiter along the section line A-A of FIG. 1.

FIG. 3 is a cross-sectional view of the downhole torque limiter along the section line B-B of FIG. 2.

FIG. 4 is a partial sectional view of the downhole torque limiter in accordance with another embodiment.

FIG. 5 is a detail view of the portion designated as “C” of FIG. 4.

FIG. 6 is a partial sectional view of the downhole torque limiter in accordance with another embodiment.

FIG. 7 is a detail view of the portion designated as “D” of FIG. 6.

FIG. 8 is a detail view of the portion designated as “E” of FIG. 6.

FIG. 9 is an elevation view of the downhole torque limiter in accordance with a preferred embodiment, wherein the downhole torque limiter is positioned below a downhole motor.

FIG. 10 is a detail view of the portion designated as “F” of FIG. 9.

FIG. 11 is an elevation view of the downhole torque limiter in accordance with a preferred embodiment, wherein the downhole torque limiter is positioned above a downhole motor.

FIG. 12 is a detail view of the portion designated as “G” of FIG. 11.

FIG. 13 is an elevation view of the downhole torque limiter disposed within a well bore, in accordance with a preferred embodiment.

FIG. 14 is a detail view of the portion designated as “H” of FIG. 13.

FIG. 15 is a detail view of the portion designated as “J” of FIG. 14.

While the invention may be subject to modifications and various forms, specific embodiments are shown by way of example in the drawings and will herein be described in detail. It should be understood that the drawings and detailed descriptions presented herein are not intended to limit the invention to a particular form or embodiment disclosed. On the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 1. General Features

Referring to FIGS. 1-15, there is shown a downhole torque limiter 38 in accordance with various embodiments. As used herein, the terms “a” or “an” shall mean one or more than one. The term “plurality” shall mean two or more than two. The term “another” is defined as a second or more. The terms “including” and/or “having” are open ended (e.g., comprising). The term “or” as used herein is to be interpreted as inclusive or meaning any one or any combination. Therefore, “A, B or C” means “any of the following: A; B; C; A and B; A and C; B and C; A, B and C”. An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive.

Reference throughout this document to “one embodiment,” “certain embodiments,” “an embodiment,” or similar term means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearances of such phrases in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner on one or more embodiments without limitation.

Generally, in a preferred embodiment, the downhole torque limiter 38 comprises an outer tubular collar 6, an upper housing 2, compression assemblies 5, 12, anti-rotation plates 7, 8, a ring assembly 9, 11, an inner mandrel 16, and a lower end cap 14. The inner mandrel 16 generally extends through a bore 4 of the outer collar 6 and is adapted to accept a bit 39 or other threaded component at a lower end. The upper housing 2 is coupled to the outer collar 6.

The inner components 5, 7, 8, 9, 11, 12, 16 are restrained within the outer collar 6 by the upper housing 2 and a lower end cap 14. The upper housing 2 and lower end cap 14, along with other components maintain the compression assemblies 5, 12 in a state of compression.

The compression assemblies 5, 12 provide compressive force against the alternating anti-rotation plates 7, 8. The anti-rotation plates 7, 8 engage features on the outer collar 6 and inner mandrel 16. Friction between the plates 7, 8 enables the transmission of torque from the outer collar 6 to the inner mandrel 16.

The downhole torque limiter 38 may be oriented within the bottom hole assembly below the downhole motor 37 and above the bit 39. In this application the downhole torque limiter 38 will not allow torque fluctuations and excessive torque to be transmitted from the bit 39 to the downhole motor 37. Alternatively, the downhole torque limiter 38 may also be oriented at any point within the drill string 35 where it is desired to limit the maximum torque transmission.

The downhole torque limiter 38 may be utilized in a variety of applications, including those in which a high capacity inline torque limiter 38 may be required. The downhole torque limiter 38 may be immersed in lubricant or working fluid of virtually any consistency.

2. Specific Embodiments

Referring to FIG. 1, there is shown the downhole torque limiter 38 in accordance with a preferred embodiment. An upper threaded connection 1 provides attachment to a portion of a drill string 35. The upper threaded connection 1 may be an integral portion of the outer collar 6 or comprise a portion of a tubular upper housing 2 which is then preferably connected to the outer collar 6 via another threaded connection 3.

The tubular upper housing 2, upon insertion into the outer collar 6, comprises a cavity or bore 4 comprising the upper portion of the inner mandrel 16. The cavity or bore 4 comprises a means of sealing fluids, therefore, only permitting flow through an inner mandrel bore 15. Sealing may be performed by any well-known method suitable for such applications, such as elastomeric rings, metal-metal contact or labyrinth seal, amongst others.

The tubular upper housing 2 comprises an internal shoulder 29 which abuts with an upper spring 5 or spring assembly 5 comprising a coil spring 5, a disc ring 5, a disc spring stack 5, hydraulic assemblies 5, or any combination of suitable items. This upper spring 5 or spring assembly 5, preferably, then abuts an outer friction plate 7 such that the spring 5 or spring assembly 5 is somewhat compressed or preloaded.

The uppermost outer friction plate 7 axially abuts an inner friction plate 8. A plurality of such plates 7, 8 may similarly alternate until preferably terminated by a final outer friction plate 7. The final or lowest outer friction plate 7 may then axially abut a ring 9 of a ring assembly 9, 11.

The ring assembly 9, 11, comprises the ring 9 and a static ring 11. The ring 9 is preferably coupled to the inner mandrel 16 via a threaded connection 10. However, the ring 9 may be coupled to the inner mandrel with a pin or other fastener, mechanical fit or various other common arrangements. The ring 9 axially rests against the static ring 11 which is preferably rotatably coupled with the outer collar 6. Although rotatably coupled with the outer collar 6, the static ring 11 is slidingly positioned within the outer collar 6, such that upon sufficient force thereupon, the static ring slides vertically (parallel to the outer collar 6) within the outer collar 6. In a preferred embodiment, the static ring 11 abuts a lower spring 12 or spring assembly 12 comprising a coil spring 12. However, other compression assemblies 12 may be used such as a disc spring, a disc spring stack 12, hydraulic assemblies 5, or any combination of suitable items. The lower spring 12 or spring assembly 12 is then preferably compressed or preloaded by contact between its upper and lower extremities with the static ring 11 and the lower end cap 14. The lower end cap 14 preferably comprises a tubular member with a bore 4 of sufficient size to allow for passage of the inner mandrel 16. The lower end cap 14 may be fixed to the outer collar 6 via a threaded connection 13 or by various other well known methods.

A threaded connection 17 is preferably provided within the lower portion of the lower mandrel 16. This connection 17 may be internal or external and will allow for connection of the inner mandrel 16 to a portion of the drill string 35 or other device.

The dual spring assemblies 5, 12 of the preferred embodiment maintain a generally constant pressure on the friction plate assembly 7, 8. For example, a downward axial force on the device 38 against the earth may cause the inner mandrel 16 to move upward. The upward movement of the inner mandrel 16, in turn moves the ring 9 which is threadedly coupled to the inner mandrel 16. As the ring 9 is in communication with the friction plate assembly 7, 8, the friction plate assembly 7, 8 moves vertically (parallel to the inner mandrel) upon movement of the inner mandrel 16. Therefore, an upward vertical movement of the friction plate assembly 7, 8 causes the lower spring 12 to become at least partially relieved from compression and increases compression of the upper spring assembly 5. Thus, the axial pressure on the friction plates 7, 8 remains constant.

Referring to FIGS. 1 & 2, the arrangement between the outer friction plate 7 and outer collar 6 is shown. A polygonal internal profile 19 preferably extends throughout the inner length of the outer collar 6. Each outer friction plate 7 therefore may contain a matching polygonal external profile such that when disposed within the outer collar 6 the outer friction plates 7 are not permitted to rotate with respect to the outer collar 6. It will be appreciated than many alternative means of rotatably securing the outer friction plate 7 to the outer collar 6 may be used such as splines, gears, key and keyways, amongst many others. The outer friction plates 7 may preferably comprise a round or other internal profile 20 to provide clearance between the outer friction plate 7 and inner mandrel 16, such that the plate 7 does not contact the inner mandrel 16.

Referring to FIGS. 1 & 3, the arrangement between inner friction plate 8 and the inner mandrel 16 is shown. A polygonal external profile 23 preferably extends along a portion of the inner mandrel 16. The inner friction plates 8 may contain matching internal polygonal profiles 23 which when disposed onto the inner mandrel 16 cause the inner friction plates to be rotatably fixed to the inner mandrel 16. It will be appreciated than many alternative means of rotatably securing the inner friction plates 8 to the inner mandrel 16 may be used such as splines, gears, key and keyways, amongst many others. The inner friction plates 8 may preferably comprise a round or other external profile 22 to provide clearance between the inner friction plate 8 and outer collar 6, such that the plate 8 does not contact the outer collar 6.

Referring to FIGS. 4 and 5, there is shown is a partial sectional view of the downhole torque limiter 38 in accordance with another embodiment. In this embodiment, the device 38 comprises a jam nut 25 arrangement. In this embodiment, the upper housing 2 is secured against the spring assembly 5 by the jam nut 25. The jam nut 25 comprises an internally threaded portion that corresponds with the external threads 27 of the upper housing 2. Upper housing 2 is threaded into outer collar 6 to a desired position such that upper housing 2 provides compressive force on the spring assembly 5, which, in turn, provides compressive force against the alternating friction plates 7, 8. Jam nut 25 is tightened against an outer collar shoulder 26. The interaction between jam nut 25 and the outer collar 6 inhibits upper housing 2 movement and maintains the desired amount of compression on spring assembly 5.

Referring to FIGS. 6, 7 and 8, there is shown is a partial sectional view of the downhole torque limiter 38 in accordance with another embodiment. In this embodiment, the device 38 comprises a shimming arrangement. Referring to FIG. 7, in this embodiment, one or more shims 30 are positioned between an internal shoulder 29 of the upper housing 2 and an upper portion 31 of spring assembly 5. When upper housing 2 is threaded into outer collar 6 against shim 30, compressive force is applied to spring assembly 5, which, in turn, provides compressive force against the alternating friction plates 7, 8. Depending on the application, additional shims 30 may be inserted between upper housing 2 and spring 5 to increase the amount of spring 5 compression. Conversely, spring 5 compression may be decreased by removing some or all of the shims 30. The shims 30 are generally tubular in shape and, in the preferred embodiment, are formed from steel. However, the shims 30 may be of different configurations and may be formed from any other suitable material capable of transferring the compressive force of the upper housing 2 to the spring 5.

Referring to FIG. 8, in this embodiment, one or more shims 30 are positioned between the lower end cap 14 and a lower portion 32 of spring 12 or spring assembly 12. When the lower end cap 14 is threaded into outer collar 6 against shim 30, compressive force is applied to spring assembly 12, which, in turn, provide compressive force against static ring 11, ring 9, and the alternating friction plates 7, 8. Depending on the application, additional shims 30 may be inserted between the lower end cap 14 and spring 12 to increase the amount of spring 12 compression. Conversely, spring 12 compression may be decreased by removing some or all of the shims 30.

The operation and use of the downhole torque limiter 38 of the preferred embodiment will now be described. In the preferred embodiment, the downhole torque limiter 38 is assembled such that, under normal torque conditions, the outer collar 6 and inner mandrel 16 rotate at the same rate. In assembly, a predetermined amount of compression is preloaded on the upper and lower spring assemblies 5, 12. In practice, this is an iterative process in which an estimate is made of the spring 5, 12 compression required to allow relative rotation of the inner mandrel 16 and the outer collar 6 (“slip point”) upon stall or near stall of the downhill motor 37. It is preferred that this slip point be reached at approximately 80% of the torque capacity (“stall torque”) of the downhole motor 37. Although the preloading compression values vary depending upon the torque capacity of the downhole motor 37 and other variables, in many applications the spring assemblies 5, 12 are preloaded such that the slip point is set at an inner mandrel 16/ outer collar 6 torque ranging from an extreme low of approximately 300-400 foot/lbs. to highs in the tens of thousands of foot/lbs. Thus, for example, if the inner mandrel 16 rotation should cease, as may occur if the bit 39 becomes stuck, the torque imparted by the outer collar 6 on the inner mandrel 16 will likely exceed 300-400 foot/lbs. If the torque limiter slip point were set at such a low threshold, the friction between plates 7, 8 will be overcome and the outer collar 6 will continue to rotate as the inner mandrel 16 rotation slows or ceases.

In assembly, the compression on each spring assembly 5, 12 is roughly adjusted by inserting or removing shims 30 between upper housing 2 and spring 5 and between lower end cap 14 and spring 12. The downhole torque limiter 38 is then put under torque conditions to determine the slip point, and, if necessary, fine adjustments are made to each spring assembly 5, 12 as described herein such that the desired compression is reached.

Upon assembling the downhole torque limiter 38, the device 38 may be used in a desired downhole environment. Referring to FIGS. 9 & 10, the downhole torque limiter 38 may be oriented within the bottom hole assembly below the downhole motor 37 and above the bit 39. In this application the downhole torque limiter 38 will not allow torque fluctuations and excessive torque to be transmitted from the bit 39 to the downhole motor 37.

Referring to FIGS. 11 & 12, alternatively, the downhole torque limiter 38 may be positioned above a downhole motor 37, or, referring to FIGS. 13-15, the downhole torque limiter 38 may be oriented at any point within the drill string 35 where it is desired to limit the maximum torque transmission.

Although, it has been shown that the downhole torque limiter 38 may be used in downhole applications comprising a downhole motor 37 and a drill bit 39, the torque limiter 38 is not limited to such applications. For example, some downhole operations involve “fishing” or efforts to retrieve pieces of pipe or tools that have become stuck in the well. Although such operations often require specialized attachments to grab and lift items from the well, the drill string 35 used in these operations often does not comprise a downhole motor 37 or drill bit 39. However, the drilling conditions may still result in undesirable levels of torque being placed on portions of the drill string 35. To address potential torque issues, the torque limiter 38 may be positioned within a wide variety of drill string 35 makeups, including those that do not comprise a downhole motor 37 or a drill bit 39.

The downhole torque limiter 38 may be utilized in a variety of applications, including those in which a high capacity inline torque limiter 38 may be required. The downhole torque limiter 38 may be immersed in lubricant or working fluid of virtually any consistency.

While there has been illustrated and described what is, at present, considered to be a preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the invention. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the invention, but that the invention will include all embodiments falling within the scope of the appended claims. For example, the connections, 1, 17 may be appropriately switched on the upper end of the housing 2 and the downhole end of the inner mandrel 16. The downhole torque limiter 38 could be completely inverted or various internal components moved while providing similar function without departing from the scope and spirit of the invention. 

1. A downhole torque limiter comprising an outer housing, a friction plate assembly, and an inner mandrel, said friction plate assembly comprising one or more outer friction plates and one or more inner friction plates, said outer housing comprising a bore and being rotatably coupled to at least one of said outer friction plates, said inner mandrel being positioned within said bore and being rotatably coupled with at least one of said inner friction plates, and at least one of the outer friction plates being frictionally engaged with at least one of the inner friction plates.
 2. The downhole torque limiter of claim 1 further comprising one or more compression assemblies structured and arranged to provide a compression of said friction plate assembly.
 3. The downhole torque limiter of claim 2, the compression assemblies comprising an upper spring assembly and a lower spring assembly, said friction plate assembly being positioned between said upper and lower spring assemblies.
 4. The downhole torque limiter of claim 3 further comprising an upper housing coupled to the outer housing, wherein said upper spring assembly is positioned between the upper housing and the friction plate assembly.
 5. The downhole torque limiter of claim 3 further comprising a lower end cap coupled to the outer housing, the lower spring assembly being positioned between said lower end cap and the friction plate assembly.
 6. The downhole torque limiter of claim 5 further comprising a ring assembly, said ring assembly being positioned between said lower spring assembly and said friction plate assembly, and said ring assembly comprising an inner mandrel ring and a static ring, said inner mandrel ring being rotatably coupled to the inner mandrel, said static ring being rotatably coupled to the outer housing.
 7. The downhole torque limiter of claim 3 wherein the compression is adjustable.
 8. The downhole torque limiter of claim 7 further comprising one or more jam nuts for adjusting said compression.
 9. The downhole torque limiter of claim 7 further comprising one or more shims for adjusting said compression.
 10. The downhole torque limiter of claim 9, at least one of said shims being positioned between the lower spring assembly and the lower end cap.
 11. The downhole torque limiter of claim 1, the friction plate assembly being vertically slideable in relation to said outer housing.
 12. The downhole torque limiter of claim 1, the inner plates arranged in an alternating pattern with such outer plates.
 13. A method of preventing damage to downhole drilling equipment comprising the steps of: providing a torque limiting device and downhole equipment; said torque limiting device comprising an outer housing, a friction plate assembly, and an inner mandrel, said friction plate assembly comprising one or more outer friction plates and one or more inner friction plates, said outer housing comprising a bore and being rotatably coupled with at least one of said outer friction plates, said inner mandrel being positioned within said bore and being rotatably coupled to at least one of said inner friction plates, and at least one of the outer friction plates being frictionally engaged with at least one of the inner friction plates; said downhole equipment comprising a drill string; and coupling said downhole torque limiting device to said drill string.
 14. The method of preventing damage to downhole drilling equipment of claim 13, the downhole equipment further comprising a downhole motor, and a drill bit, wherein the step of coupling said downhole torque limiting device to said drill string further comprises positioning the device, in relation to the earth, below the downhole motor and above the drill bit.
 15. The method of preventing damage to downhole drilling equipment of claim 14, wherein said downhole torque limiting device is positioned above the downhole motor.
 16. The method of preventing damage to downhole drilling equipment of claim 14, the drill string comprising a plurality of joints, wherein said downhole torque limiting device is positioned above the downhole motor such that at least one of said joints is positioned between the downhole torque limiting device and the downhole motor. 